Low-pressure mercury vapor discharge lamp

Abstract

A low-pressure mercury vapor discharge lamp comprises a discharge vessel ( 10 ) having a tubular portion ( 11 ). The discharge vessel ( 10 ) encloses a discharge space ( 13 ) provided with a filling of mercury and a rare gas in a gastight manner. The tubular portion ( 13 ) of the discharge vessel ( 10 ) is provided with a metal oxide layer ( 15 ) and a luminescent layer ( 17 ) on a surface ( 14 ) facing the discharge space ( 13 ). The discharge lamp comprises means for maintaining an electric discharge in the discharge vessel ( 20 b ). The discharge lamp is characterized in that the luminescent layer ( 17 ) comprises an alkali metal oxide. This alkali metal oxide is preferably sodium oxide and/or potassium oxide, and the concentration of the alkali metal oxide is 0.002≦Na 2 O≦0.1% by weight and/or 0.002≦K 2 O ≦0.1% by weight. The tubular portion ( 11 ) of the discharge vessel ( 10 ) preferably has a further metal oxide layer which acts as an alkali metal-repellent layer. This further metal oxide layer preferably comprises silicon oxide. The lamp according to the invention has a comparatively low mercury consumption.

What is claimed is:  
     
       1. A low-pressure mercury vapor discharge lamp comprising a discharge vessel ( 10 ) with a tubular portion ( 11 ) which is transmissive to radiation generated in the discharge vessel ( 10 ), 
       said discharge vessel ( 10 ) enclosing a discharge space ( 13 ) provided with a filling of mercury and a rare gas in a gastight manner,  
       the tubular portion ( 11 ) of the discharge vessel ( 10 ) being provided with a metal oxide layer ( 15 ) and a luminescent layer ( 17 ) on a surface ( 14 ) facing the discharge space ( 13 ),  
       the low-pressure mercury vapor discharge lamp comprising discharge means ( 20   b ) for maintaining an electric discharge in the discharge vessel ( 10 ), characterized in that  
       the luminescent layer ( 17 ) comprises an alkali metal oxide.  
     
     
       2. A low-pressure mercury vapor discharge lamp as claimed in  claim 1 , characterized in that the alkali metal oxide in the luminescent layer ( 17 ) comprises sodium oxide and/or potassium oxide, in which the concentration of alkali metal oxide is 0.001≦Na 2 O≦0.2% by weight and/or 0.001≦K 2 O≦0.2% by weight. 
     
     
       3. A low-pressure mercury vapor discharge lamp as claimed in  claim 2 , characterized in that the concentration is 0.002≦Na 2 O≦0.1% by weight and/or 0.002≦K 2 O≦0.1% by weight. 
     
     
       4. A low-pressure mercury vapor discharge lamp as claimed in  claim 1 , characterized in that the metal oxide layer ( 15 ) comprises at least an oxide of at least an element from the group of magnesium, aluminum, titanium, zirconium, and the rare earths. 
     
     
       5. A low-pressure mercury vapor discharge lamp as claimed in  claim 4 , characterized in that said metal oxide layer ( 15 ) comprises aluminum oxide and/or yttrium oxide. 
     
     
       6. A low-pressure mercury vapor discharge lamp as claimed in  claim 1 , characterized in that the tubular portion ( 11 ) of the discharge vessel ( 10 ) has a further metal oxide layer ( 16 ) between the surface ( 14 ) facing the discharge space and the metal oxide layer ( 15 ). 
     
     
       7. A low-pressure mercury vapor discharge lamp as claimed in  claim 6 , characterized in that the further metal oxide layer ( 16 ) comprises silicon oxide. 
     
     
       8. A low-pressure mercury vapor discharge lamp as claimed in  claim 1 , characterized in that the luminescent material comprises a mixture of green-luminescing, terbium-activated cerium magnesium aluminate, cerium aluminate or cerium lanthanum phosphate, blue-luminescing, europium-activated barium magnesium aluminate or a strontium halophosphate or a strontium halophosphate, and red-luminescing yttrium oxide activated by trivalent europium.